The invention relates to a method and apparatus for regulating the admission of fluids into the interior of and the evacuation of fluids from chambers wherein the fluids are maintained at an elevated pressure. More particularly, the invention relates to improvements in a method and apparatus for building up and reducing the pressure of a gaseous fluid in a chamber wherein a dielectric receptor sheet is exposed to object-modulated X-rays while the pressure of fluid in the chamber exceeds atmospheric pressure.
Commonly owned copending application Ser. No. 829,960 filed Sept. 1, 1977 by Jurgen Muller et al. for "Ionography imaging method and chamber" discloses a system which admits a high Z gas into the interelectrode gap of an ionography imaging chamber upon introduction of a dielectric receptor sheet into the gap and evacuates the gas prior to removal of the dielectric receptor sheet from the gap. The system employs a container which constitutes or includes a bellows and is connected with the interelectrode gap of the ionography imaging chamber upon completion of the exposure of a dielectric receptor sheet to object-modulated radiation. The highly compressed gas flows from the gap into the container whereby the latter expands and the pressure of the gas decreases. When the pressure in the gap is reduced to atmospheric pressure, the chamber is opened to allow for withdrawal of a receptor sheet which bears a latent image of the X-rayed object. The gap then receives a fresh receptor sheet and a pump is started to return the gas from the container into the interelectrode gap. Such circulation of the gas along a path which is practically completely sealed from the atmosphere is desirable and necessary in order to avoid losses of expensive gas, e.g., Xenon, Krypton or Freon. A drawback of the just described system is that the evacuation of gas from the interelectrode gap and the reintroduction of gas into the gap takes up a substantial amount of time. Moreover, the system must employ a relatively large expandible container, especially if the pressure of gas during exposure of a dielectric receptor sheet to object-modulated radiation is rather high. Such pressure can be as high as 20 atmospheres.